1. Field of the Invention
The present invention relates to a method of determining respective segment times between corresponding pairs of equally spaced marks provided on a rotating body, especially a transducer disk, connected to a camshaft of an internal combustion engine.
2. Prior Art
For regulating internal combustion engines, the rpm of the crankshaft and/or camshaft of the engine is always needed. From the position of these shafts, when trigger signals for certain components must be generated can be determined. For example, the time when current must be supplied to a particular injection valve so that the most optimal possible combustion event can proceed in the associated cylinder is dependent on the position of the crankshaft and/or camshaft of a Diesel engine.
To determine the angular position of the crankshaft and/or camshaft of an internal combustion engine, sensors are typically used that each scan a transducer wheel connected to the crankshaft and the camshaft, respectively. The two transducer wheels typically have a characteristic sequence of angle markings or slits on their circumference. As these angle markings or slits move past the stationary sensors, voltages are induced in the sensors, and from the course of these voltages over time, the surface area of the applicable transducer disk can be derived. The sensor voltages are typically converted into square-wave signals to make them easier to evaluate. The position of each of the signal edges corresponds to a certain rpm of the crankshaft or camshaft.
In Diesel engines currently in use, the transducer disk connected to the crankshaft, in a rotating cylinder engine, has 60-3.multidot.2 teeth, and the distribution of the teeth or angle markings is such that three gaps are formed, and between each two gaps there are 18 teeth, spaced apart by equal angles from one another. The disk connected to the camshaft has six slits, for six cylinders, and the slits are spaced apart by equal angles. A seventh slit is disposed between the first and second slits and serves as a reference marking; it is only slightly distant from the first slit, for instance by a camshaft angle of 15.degree..
When the engine is started, it is brought to a starting rpm with the aid of a starter. The crankshaft and the camshaft then rotate at a relatively constant rpm; it is well known that the crankshaft rotates at twice the speed of the camshaft. No later than after one revolution of the camshaft, a synchronization can be effected, since the seventh tooth is recognized as the synchronizing tooth. From this instant on, during normal operation, the correct injection can be begun. The requisite trigger signals are output by the engine control unit, which processes the output signals of the sensors. For instance, the engine control unit trips the delivery of current to the injection valves or the onset of pumping at the correct instant, thus enabling optimal regulation of the engine. Since the transducer disk on the crankshaft has many teeth, a signal is produced that has pulses in rapid succession; exact engine regulation is thus possible, in the normal situation. If under unfavorable conditions the crankshaft sensor fails, emergency operation should be possible with the camshaft sensor alone.